code: def save(self, checkpoint):
      if not self.model_built:
          invalidInputError(
              False,
              "You must call fit_eval or restore first before calling save!",
          )
      state_dict = self.state_dict()
      with open(checkpoint, "wb") as f:
          SafePickle.dump(state_dict, f)
  
imports: from bigdl.orca.automl.model.abstract import BaseModel, ModelBuilder
  import numpy
  from bigdl.orca.automl.metrics import Evaluator
  from bigdl.orca.common import SafePickle
  import copy
  import tensorflow
  from tensorflow.keras import backend
  import types
  from bigdl.dllib.utils.log4Error import *
label_desc: Use image node_id 10 for calling the KerasBaseModel obj's underlying member method code with example usage: obj.save(checkpoint) without return types